The Flow Of Gases In Furnaces

APPENDIX VII

Gas Checker
Air Checker

Temp, products of combustion at bottom of checker-work, degrees C ....... ....................
800
600

Products of combustion per cu meter of gas burnt, cu m . . Products of combustion == 0 90+1 78= .......
0.90 2
1.78 68

Average temperature products of combustion = [(800X0 90) + (600X1 78)] -^ 2 68 ............
6(
>5

(No allowance is made for a heat loss in the flues, although in practice a
temperature drop of 50° to 100° will occur between the bottom of the checker-
work and the boiler inlet. The heat capacities given by the curves are
based on the consumption of 100 molecular volumes or 2.232 cu m. of gas.
These values have been reduced to those for a cubic meter of gas burnt in
this computation.)
Heat capacity products of combustion of 1 cu m of gas
at the bottom of the checkerwork, average £ = 665,
calories........................................ 635
Heat capacity products of combustion of 1 cu m of gas
at the boiler outlet, average 2=200, calories........ 162
Heat available for production of steam, calories......473
Assuming that one-third of this heat will be lost in flues
and boiler setting, net amount of heat available will
be, calories..................................... 316
Heat required for evaporation of 1 kg of water at 5.54
kg per sq cm absolute (78.76 Ib per sq in) = 156+500,
calories........................................ 656
Products of combustion from 1 cu m of gas will evapo-
rate: 316-^656, kg.............................. 0.481
1 sq m of boiler heating surface is equivalent to the
evaporation of 15 kg of water per hour; or 0.00417 kg
of water per second
Area of the heating surface required to evaporate 0.481
kg of water per second will be: 0.481 -f-0.00417 sq m. 116
(This being the area of the heating surface required to
absorb the heat in the products of combustion from
1 cu m of the gas burnt)
As the average amount of gas burnt per second is 1.75
cu m, the area of the heating surface required will be:
116.00X1.75................................... 203
Quantity of gas burnt per second, p. 231.